TISSUES, ORGANS, AND SYSTEMS. 



01 



Fig. 35. 



Fig. 36. 



are generally enlarged at regular intervals, so that they appear 

 to consist of a series of many portions, and give a transversely 

 striated aspect to 

 the muscular fibres, 

 or they appear more 

 even, and then the 

 primitive bundles 

 present a longitu- 

 dinal striation. Be- 

 sides these fibrils, 

 the muscular fibres 

 contain nothing but 

 a small quantity of 

 the viscid substance 

 uniting them, and a 

 certain number of 

 rounded or elon- 

 gated cell-nuclei, 

 which generally lie 

 against the inner 

 surface of the sar- 

 colemma. The association of the muscular fibres into muscles 

 and muscular membranes occurs in such a manner that they 

 either apply themselves parallel to one another, or are united 

 into true networks of transversely striated muscles. They then 

 receive an investment of more delicate or firmer connective 

 tissue, the so-called perimysium, with which finer elastic fibres 

 and also fat-cells are frequently mingled ; and are, besides, 

 surrounded by numerous blood-vessels and nerves. 



In chemical characters the principal substance of the trans- 

 versely striated muscular fibres agi'ees perfectly with the syntonin 

 referred to in the previous section. The sarcolemma is very 

 resistant to acids and alkalies, whilst the nuclei present the 

 common characters of those organs. A fluid with an acid 

 reaction may be expressed from the muscles, in which Liebig 

 and Scherer have discovered an interesting series of non- 

 Fig. 35. Two muscular fibres of man, x 350. In the one the bundle of fibrils, b, 

 is torn, and the sarcolemma, a, is to be seen as a mere empty tube. 



Fig. 36. Primitive fibrils from a primitive bundle of the Axolotl (Siredon 

 piseiformk); a, a small bundle of them ; /', an isolated fibril, x 600. 



